The present invention relates to an ultrathin cylinder having a short axial length.
A cylinder having a piston for sliding in a cylinder bore by operation of fluid pressure and a piston rod connected to the piston is already known.
In this known cylinder, in general, the piston is housed in a cylinder bore with opposite ends thereof closed with end plates, the piston rod having a smaller diameter than the piston is connected to a central portion of the piston, the piston rod extends outside through one of the end plates, and the piston rod is supported by the end plate through a bearing or the like such that the piston rod and the piston can smoothly slide on each other.
In the known cylinder, however, the piston has a length required for s table sliding, axial lengths of the end plates are large, and the bearing for supporting the piston rod is provided. Therefore, an axial length of the cylinder necessarily becomes long and there is a limit to reducing the length to form the cylinder into a thin type. In order to form the cylinder into the thin type, an axial length of the piston needs to be reduced, for example. However, if the piston is thinned, the piston becomes liable to tilt and cannot slide smoothly. If the end plates are thinned or the bearing is eliminated, an axis of the piston tilts and scratches become liable to be caused by galling.
The present inventor found that tilting of a piston could be reliably prevented even if a cylinder was thin and that the cylinder with excellent sliding stability could be obtained by forming the piston into a short cylindrical shape and causing the piston to also function as a piston rod and accomplished the present invention.
Therefore, it is an object of the invention to provide an ultrathin cylinder having a short cylindrical piston.
It is another object of the invention to provide an ultrathin cylinder in which a piston does not tilt and slides stably.
To achieve the above objects, according to the invention, there is provided an ultrathin cylinder comprising: a short columnar cylinder body having a cylinder bore with an axial length smaller than its radius and a bore cover with which an end of the cylinder bore is closed; a piston having a cylindrical portion sliding in the cylinder bore, an end wall with which a base end portion of the cylindrical portion is closed, and a guide hole formed at a center of the end wall, with the cylindrical portion also functioning as a rod; a guide rod fixed to a central portion of an inner face of the hole cover of the cylinder body and passing for sliding through the guide hole of the piston to extend into the cylindrical portion; a rod cover fixed to a tip end of the guide rod in the cylindrical portion to slide in the cylindrical portion; a first pressure chamber formed between the cylinder body and the piston in the cylinder bore and a second pressure chamber formed between the piston and the rod cover in the cylindrical portion; and a first port and a second port individually communicating with the first pressure chamber and the second pressure chamber.
In the ultrathin cylinder having the above structure, because the piston is in the short cylindrical shape, also functions as the piston rod, and has an outer peripheral face supported by the cylinder body, an inner peripheral face supported by the rod cover, and a central portion supported by the guide rod, the piston slides while being supported in three points. Therefore, tilting of the piston is prevented and the piston operates stably and smoothly, though the cylinder is the ultrathin cylinder having the axial length smaller than its radius.
According to a concrete structural form of the invention, the cylinder further comprises a first wear ring for guiding sliding of an outer peripheral face of the cylindrical portion of the piston and a cylinder bore on each other and a second wear ring for guiding sliding of an inner peripheral face of the cylindrical portion and the rod cover on each other, wherein the wear rings are disposed in different positions in an axial direction of the piston.
Because the wear rings as shaft supporting means are provided to two positions concentric with each other to have different diameters on an outer peripheral side and an inner peripheral side of the piston and are disposed in different positions in the axial direction of the piston, the piston is supported more reliably by the wear rings and slides stably. As a result, it is possible to make the cylinder thinner. Because strength of a bearing is determined by a projected area, an axial length of the shaft supporting means can be suppressed by increasing diameters of the wear rings as compared with the length of the cylinder and the cylinder can be thinned effectively.
According to a further concrete structural form of the invention, a first sealing member for providing sealing between the outer peripheral face of the cylindrical portion of the piston and the cylinder bore and the first wear ring are provided to the outer peripheral face of the cylindrical portion, a second sealing member for providing sealing between the inner peripheral face of the cylindrical portion and the rod cover and the second wear ring are provided to the outer peripheral face of the rod cover, the first wear ring is disposed in a position closer to the rear end portion of the piston than the first sealing member, and the second wear ring is disposed in a position closer to a tip end portion of the piston than the second sealing member.
According to another concrete structural form of the invention, the guide rod and the rod cover have a plurality of bolt insertion holes in positions corresponding to each other, an end wall of the cylinder body has a plurality of screw holes, and the guide rod and the rod cover are fixed to the end wall by common bolts screwed down into the screw holes from a side of the rod cover through the respective bolt insertion holes.
If the ultrathin cylinder of the invention is used as a power source of a small press, a lifter for a transfer line, or the like, because of the ultrathin cylinder, the press, the lifter, or the like can be miniaturized and large driving force can be obtained in spite of the small size because large pressure receiving areas of the piston can be obtained.